Different from a regular Doom level, the map first has the player solve several puzzles with no combat, then unleashes a number of arch-viles that the player must kill or evade on his way back to the exit. It is set in some sort of an ancient temple of green marble, with climbable vines on the walls. The only weapon that can be found on the map is the BFG9000, one being hidden in each of the secret areas.

Get onto the ledge by climbing the vines (by walking up against the wall as if you walked up stairs) and approach the blue key. A door will open; head down the winding stairs, past the crushers, and press the skull key to lower the lift. Jump down into the central hub.

Use the skull switch to the north-west and go down the lift. Head down the ledge, quickly running past the lava; be careful about the crushers that will trigger near the end of the passage. Press the skull switch at the end, then leave the same way and get back to the central hub.

Now the next part of the level is accessible. Press the south-western skull switch in the hub, then head down. Approach the southern wall to lower a part of the floor. Enter the hole, press the skull switch and get back on the floor section before it rises (you need to press the switch right before leaving the hole). The switch will temporarily reveal another hole to the east of the room; enter and press the switch inside. Leave back into the room, and you will see a set of stairs has appeared, leading to the final skull switch here. Press it, then head back to the hub.

Now you can access the final part. Head down the south-eastern passage, climbing the vines on the way, and open the wall at the end. In the next room, you need to catch onto the vines on the wall to the east of the door; to do this, stay as close to the wall as possible (if you fall off, use the other set of vines to climb up and back onto the ledge). Make your way to the skull switch which will raise an invisible bridge. Go back to the starting ledge and go across the bridge, press the final skull switch, jump out and climb the vines out of the lava. Head back to the central hub.

The blue skull key has been revealed. Picking it up will teleport a number of arch-viles into the map.

Head back to the north-western section of the hub (all other paths are barred off). Get past the crushers and press the skull switch at the end again. Now go to the north-eastern end of the hub, and make your way back to the beginning of the level. The arch-viles are unable to follow you up the winding stairway, so the ledge at the end makes for a good place to catch your breath. Jump down and very carefully approach the blue key bars; as soon as the two final arch-viles teleport in, climb back onto the ledge to avoid their attack. Once they are dead, open the bars and enter the exit.

In the starting room, there are several lion heads on the wall, one of which has a glowing eye visible in its mouth. Shoot the eye (to pull this off, you need to stand at the topmost step of the thin, invisible "stairs" which constitute the climbable vine) and a section of the lava stream will lower, allowing you access to a BFG9000 and four energy cells. (sector 32)

In the hub area, three arrows can be seen in the western lava pool. Step into the area between the arrows to find a BFG9000. (sector 274)

In the first puzzle section (the westernmost area of the level), there is a BFG9000 and two cell charges sitting on a pillar in the pool of lava. When you press a skull switch to lower the lift leading to this area from the hub, that pillar also lowers for a moment. Run onto it quickly and claim the BFG9000. (sector 350) To get out of the lava, press the skull switch in the pool to lower an escape lift (if you are nimble enough, you can pull it off without getting damaged by the lava).

In the second puzzle section (southwestern area of the level), as you walk into the room with the lava pit, a wall with a demonic face to the north opens for a moment. Enter the niche behind it and open the northern wall to find a BFG9000. (sector 376)

After pressing the final switch in the second puzzle section, two niches with hanging corpses on the walls are revealed to the north of the room. Enter the eastern niche and activate the eastern wall to lower a lift containing a BFG9000. (sector 375)

In the third puzzle section (southeastern area of the level), head across the vines to the platform to the east, then make a running jump to the south to get the BFG9000 resting atop a marble column. To trigger the secret, you need to actually plant your feet on the column; the best way to ensure this is to stand near the vine-covered wall and run across it towards the BFG9000. (sector 198)

As you descend the winding stairway near the beginning, you pass near an opening inside of which is a dormant arch-vile. Once you have the blue key and you are coming back up the stairs, this opening can be entered (after killing its occupant, of course); inside is a BFG9000. (sector 223)